How Old is My Tree?
Estimating the age of a tree is more art than science. The following information is a guide intended to help with that process and is, at least, a 'rule of thumb'.
Trees typically are not as old as they look, and look older than they are!
With age, the height and spread of a tree reaches a maximum, and then declines. Neither height nor spread can therefore be used to estimate the age of a tree. However, the trunk increases in circumference throughout its life and it is this that can be used as a measure of age.
Most trees reach a point when fully mature and with a full crown when the circumference is 2.5cm (one inch) for each year of growth. Hence a tree that is 4.5 metres (15 feet) in circumference, measured at breast height i.e. approximately 1.5 metres (5 feet), is approximately 180 years old.
When juvenile or semi-mature, trees will add some 3.75cm (1 ½ inches) in circumference but when mature and over mature will slow down their rates of growth annually to increments of perhaps 1.8cm (¾ inch) in circumference.
Exceptions to the rule
- Trees growing in a woodland environment typically have a restricted crown and therefore increase in circumference at approximately 50% of the rate of fully crowned trees. Hence, a tree that is 2.25 metres (7 ½ feet) in circumference, measured at breast height, is approximately 180 years old.
- Fast growing trees, including most Eucalyptus, some Fir trees, Willows, Larch, Giant Sequoia and a handful of others, can add 50-75 mm (2-3 inches) in circumference.
- Slow growing trees, especially Yew, may only add 1.25cm (½ inch) in circumference per year and in their maturity possibly as little as 0.5 (1/5 inch) per year.
- Scots Pine, Horse Chestnut and Common Lime grow at the average rate for perhaps the first 100 years and then slow down to perhaps half the average rate, and possibly even less.